How the AP-GfK poll on Republican candidates was conducted

The Associated Press-GfK poll on the Republican presidential candidates was conducted by GfK Public Affairs and Corporate Communications October 15-19. It is based on online interviews of 1,027 adults who are members of GfK's nationally representative KnowledgePanel.

The original sample was drawn from respondents recruited by phone or mail survey methods. GfK provides Internet access to participants who don't already have it. With a probability basis and coverage of people who otherwise couldn't access the Internet, online surveys using KnowledgePanel are nationally representative.

Interviews were conducted in both English and Spanish.

As is done routinely in surveys, results were weighted, or adjusted, to ensure that responses accurately reflect the population's makeup by factors such as age, sex, race, education and phone use.

No more than 1 time in 20 should chance variations in the sample cause the results to vary by more than plus or minus 3.3 percentage points from the answers that would be obtained if all adults in the U.S. were polled. Some questions were asked among a half sample of respondents and have a higher margin of error.

There are other sources of potential error in polls, including the wording and order of questions.